Plasma miR-26a-5p is a biomarker for retinal neurodegeneration of early diabetic retinopathy

Serum miR-26a level is decreased in cataract patients with glaucoma and related to visual quality

CLINICAL RELEVANCE

microRNAs have been found to be involved in the progression of a variety of ocular diseases.

BACKGROUND

Cataract and glaucoma often coexist, and combined surgery is a common treatment. The aim of this study is to analyse the correlation between miR-26a and visual quality in cataract patients with glaucoma.

METHODS

Seventy patients with cataract and glaucoma and 70 healthy volunteers were enrolled and received phacoemulsification and trabeculectomy. The patients were divided into low and high miR-26a expression groups according to miR-26a mean expression. The objective scattering index, strehl ratio, and modulated transfer function cut-off were analysed by optical quality analysis system II. The changes of miR-26a, objective scattering index, strehl ratio, modulated transfer function cut-off, and the correlation between the indicators were analysed. The downstream genes of miR-26a were analysed by Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes functional enrichment.

RESULTS

There were significant differences between patients and controls in lipid biomarker levels and visual indicators. miR-26a was decreased in the patient group. Strehl ratio and modulated transfer function cut-off in the miR-26a low-expression group were lower than in high-expression group, while mean defect of the visual field and objective scattering index were higher than in high-expression group. The miR-26a expression was negatively correlated with the severity of disease and objective scattering index, and positively correlated with strehl ratio and modulated transfer function cut-off. After surgery, miR-26a, strehl ratio, and modulated transfer function cut-off were increased, and objective scattering index was decreased. The downstream genes of miR-26a were related to several biological processes and signalling pathways.

CONCLUSION

In cataract patients with glaucoma, miR-26a expression was lower than matched controls and increased following combined cataract removal and trabeculectomy.

Advances in Research Related to MicroRNA for Diabetic Retinopathy

Diabetic retinopathy (DR) is a severe microvascular complication of diabetes and is one of the primary causes of blindness in the working-age population in Europe and the United States. At present, no cure is available for DR, but early detection and timely intervention can prevent the rapid progression of the disease. Several treatments for DR are known, primarily ophthalmic treatment based on glycemia, blood pressure, and lipid control, which includes laser photocoagulation, glucocorticoids, vitrectomy, and antivascular endothelial growth factor (anti-VEGF) medications. Despite the clinical efficacy of the aforementioned therapies, none of them can entirely shorten the clinical course of DR or reverse retinopathy. MicroRNAs (miRNAs) are vital regulators of gene expression and participate in cell growth, differentiation, development, and apoptosis. MicroRNAs have been shown to play a significant role in DR, particularly in the molecular mechanisms of inflammation, oxidative stress, and neurodegeneration. The aim of this review is to systematically summarize the signaling pathways and molecular mechanisms of miRNAs involved in the occurrence and development of DR, mainly from the pathogenesis of oxidative stress, inflammation, and neovascularization. Meanwhile, this article also discusses the research progress and application of miRNA-specific therapies for DR.

miR-26a-5p Attenuates Oxidative Stress and Inflammation in Diabetic Retinopathy through the USP14/NF-κB Signaling Pathway

Purpose

Diabetic retinopathy (DR) is an ocular disease caused by diabetes and may lead to vision impairment and even blindness. Oxidative stress and inflammation are two key pathogenic factors of DR. Recently, regulatory roles of different microRNAs (miRNAs) in DR have been widely verified. miR-26a-5p has been confirmed to be a potential biomarker of DR. Nevertheless, the specific functions of miR-26a-5p in DR are still unclear.

Methods

Primary cultured mouse retinal Müller cells in exposure to high glucose (HG) were used to establish an in vitro DR model. Müller cells were identified via morphology observation under phase contrast microscope and fluorescence staining for glutamine synthetase. The in vivo animal models for DR were constructed using streptozotocin-induced diabetic C57BL/6 mice. Western blotting was performed to quantify cytochrome c protein level in the cytoplasm and mitochondria of Müller cells and to measure protein levels of glial fibrillary acidic protein (GFAP), ubiquitin-specific peptidase 14 (USP14), as well as factors associated with NF-κB signaling (p-IκBα, IκBα, p-p65, and p65) in Müller cells or murine retinal tissues. ROS production was detected by CM-H2DCFDA staining, and the concentration of oxidative stress markers (MDA, SOD, and CAT) was estimated by using corresponding commercial kits. Quantification of mRNA expression was conducted by RT-qPCR analysis. The concentration of proinflammatory factors (TNF-α, IL-1β, and IL-6) was evaluated by ELISA. Hematoxylin-eosin staining for murine retinal tissues was performed for histopathological analysis. Immunofluorescence staining was conducted to determine NF-κB p65 nuclear translocation in Müller cells. Furthermore, the interaction between miR-26a-5p and USP14 was verified via the luciferase reporter assays.

Results

HG stimulation contributed to Müller cell dysfunction by inducing inflammation, oxidative injury, and mitochondrial damage to Müller cells. miR-26a-5p was downregulated in Müller cells under HG condition, and overexpression of miR-26a-5p relieved HG-induced Müller cell dysfunction. Moreover, miR-26a-5p targeted USP14 and inversely regulated USP14 expression. Additionally, HG-evoked activation of NF-κB signaling was suppressed by USP14 knockdown or miR-26a-5p upregulation. Rescue assays showed that the protective impact of miR-26a-5p upregulation against HG-induced Müller cell dysfunction was reversed by USP14 overexpression. Furthermore, USP14 upregulation and activation of NF-κB signaling in the retinas of DR mice were detected in animal experiments. Injection with miR-26a-5p agomir improved retinal histopathological injury and weakened the concentration of proinflammatory cytokines and oxidative stress markers in the retinas of DR mice.

Conclusion

miR-26a-5p inhibits oxidative stress and inflammation in DR progression by targeting USP14 and inactivating the NF-κB signaling pathway.

A 3-miRNA Risk Scoring Signature in Early Diabetic Retinopathy

PURPOSE

The aim of our study was to investigate a comprehensive profile of streptozotocin (STZ)-induced early diabetic retinopathy (DR) mice to identify a risk scoring signature based on micorRNAs (miRNAs) for early DR diagnosis.

METHODS

RNA sequencing was performed to obtain the gene expression profile of retinal pigment epithelium (RPE) in early STZ-induced mice. Differentially expressed genes (DEGs) were determined with log2|fold change (FC)| > 1 and p value < 0.05. Functional analysis was carried out based on gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and the protein-protein interaction (PPI) network. We predicted the potential miRNAs via online tools and ROC curves were then conducted. Three potential miRNAs with AUC > 0.7 were explored via public datasets and a formula was further established to evaluate DR severity.

RESULTS

In total, 298 DEGs (200 up-regulating and 98 down-regulating) were obtained through RNA sequencing. Hsa-miR-26a-5p, hsa-miR-129-2-3p and hsa-miR-217 were three predicted miRNAs with AUC > 0.7, suggesting their potential to distinguish healthy controls from early DR. The formula of DR severity score = 19.257 - 0.004 × hsa-miR-217 + 5.09 × 10^-5 × hsa-miR-26a-5p - 0.003 × hsa-miR-129-2-3p was established based on regression analysis.

CONCLUSIONS

In the present study, we investigated the candidate genes and molecular mechanisms based on RPE sequencing in early DR mice models. Hsa-miR-26a-5p, hsa-miR-129-2-3p and hsa-miR-217 could work as biomarkers for early DR diagnosis and DR severity prediction, which was beneficial for DR early intervention and treatment.

Antioxidant Phytochemicals as Potential Therapy for Diabetic Complications

The global prevalence of diabetes continues to increase partly due to rapid urbanization and an increase in the aging population. Consequently, this is associated with a parallel increase in the prevalence of diabetic vascular complications which significantly worsen the burden of diabetes. For these diabetic vascular complications, there is still an unmet need for safe and effective alternative/adjuvant therapeutic interventions. There is also an increasing urge for therapeutic options to come from natural products such as plants. Hyperglycemia-induced oxidative stress is central to the development of diabetes and diabetic complications. Furthermore, oxidative stress-induced inflammation and insulin resistance are central to endothelial damage and the progression of diabetic complications. Human and animal studies have shown that polyphenols could reduce oxidative stress, hyperglycemia, and prevent diabetic complications including diabetic retinopathy, diabetic nephropathy, and diabetic peripheral neuropathy. Part of the therapeutic effects of polyphenols is attributed to their modulatory effect on endogenous antioxidant systems. This review attempts to summarize the established effects of polyphenols on endogenous antioxidant systems from the literature. Moreover, potential therapeutic strategies for harnessing the potential benefits of polyphenols for diabetic vascular complications are also discussed.

Noncoding RNAs Are Promising Therapeutic Targets for Diabetic Retinopathy: An Updated Review (2017-2022)

Diabetic retinopathy (DR) is the most common complication of diabetes. It is also the main cause of blindness caused by multicellular damage involving retinal endothelial cells, ganglial cells, and pigment epithelial cells in adults worldwide. Currently available drugs for DR do not meet the clinical needs; thus, new therapeutic targets are warranted. Noncoding RNAs (ncRNAs), a new type of biomarkers, have attracted increased attention in recent years owing to their crucial role in the occurrence and development of DR. NcRNAs mainly include microRNAs, long noncoding RNAs, and circular RNAs, all of which regulate gene and protein expression, as well as multiple biological processes in DR. NcRNAs, can regulate the damage caused by various retinal cells; abnormal changes in the aqueous humor, exosomes, blood, tears, and the formation of new blood vessels. This study reviews the different sources of the three ncRNAs-microRNAs, long noncoding RNAs, and circular RNAs-involved in the pathogenesis of DR and the related drug development progress. Overall, this review improves our understanding of the role of ncRNAs in various retinal cells and offers therapeutic directions and targets for DR treatment.

linc00174 deteriorates the pathogenesis of diabetic retinopathy via miR-26a-5p/PTEN/Akt signalling cascade-mediated pyroptosis

PURPOSE

We aim to investigate the potential role and underlying mechanisms of linc00174 on pyroptosis in the pathogenesis of DR.

METHODS

Expression patterns of linc00174, miR-26a-5p and PTEN in human retinal microvascular endothelial cells (hRMECs) were detected by quantitative real-time PCR (qRT-PCR) and Western blot, respectively. Biological functions of linc00174 on cell proliferation and pyroptosis were evaluated by CCK-8, flow cytometry, caspase-1 activity assays, respectively. Luciferase reporter assay was employed to verify the interaction between miR-26a-5p and linc00174/PTEN. Streptozotocin (STZ)-induced DR in mice was further constructed to verify the potential role of linc00174 in vivo. Hematoxylin and eosin (H&E) and immunohistochemical staining were performed to assess the pathological changes and caspase-1 expression in retinal tissues.

RESULTS

Up-regulated linc00174 and PTEN and down-regulated miR-26a-5p were uncovered in hRMECs treated with high glucose (HG). Mechanistically, linc00174 served as a sponge of miR-26a-5p to facilitate PTEN expression. Functionally, knockdown of linc00174 inhibited HG-induced pyroptosis of hRMECs via targeting miR-26a-5p. Moreover, linc00174/miR-26a-5p axis participated in HG-induced pyroptosis via PTEN/Akt signaling cascade. Further, silencing of linc00174 attenuated pyroptosis via regulating miR-26a-5p/PETN axis in DR mice.

CONCLUSIONS

Collectively, our study reveals that linc10074 deteriorates the pathogenesis of DR via miR-26a-5p/PTEN/Akt signalling cascade, which may shed light on the discovery of potential therapeutic agents for DR treatment.

microRNA-26a-5p Prevents Retinal Neuronal Cell Death in Diabetic Mice by Targeting PTEN

AIM

To explore the role of microRNA-26a-5p (miR-26a) in early diabetic retinal neuronal cell death and reveal the underlying mechanism(s).

METHODS

A streptozotocin (STZ)-induced diabetic mouse model was established using C57BL/6 J mice. Control or miR-26a mimic was intravitreally injected. Hematoxylin-eosin (H&E) and transmission electron microscopy (TEM) were used to observe the morphologic alterations in the retinal structure and ultrastructure, respectively. The expression of miR-26a and phosphatase and tensin homolog (PTEN) was assayed using qRT-PCR and western blotting, respectively. An immunofluorescence assay was used to investigate the distribution of PTEN expression in the retina. The expression of glial fibrillary acidic protein (GFAP) was measured to identify glial cell activation. The mRNA levels of IL-1β, NF-κB, and VEGF were examined to assess diabetic retinal inflammation.

RESULTS

miR-26a expression was decreased in retinal tissues of diabetic mice, and injection of miR-26a mimic restored the miR-26a level. Diabetic mice had significantly reduced neuroretinal thickness and ganglion cell number; miR-26a mimic delayed the thinning of neuroretinal layers and the loss of ganglion numbers. TEM showed damaged ultrastructure of retinal ganglions in diabetic mice, while miR-26a mitigated the damages. PTEN expression was increased mainly in the inner and outer nuclear layer of the retina in diabetic mice; miR-26a mimics lowered PTEN expression. GFAP, IL-1β, NF-κB, and VEGF expression were significantly increased in the diabetic mice, and intravitreal delivery of miR-26a resulted in a down-regulated expression of these factors.

CONCLUSION

miR-26a can protect against retinal neuronal impairment in diabetic mice by down-regulating PTEN, highlighting the potential of miR-26a as a target for DR treatment.